1. Field of the Invention
The present invention relates to a temperature detection device that detects a temperature of a rotor of a motor in order to protect the rotor from overheating.
2. Description of Related Art
Conventionally, in a temperature detection device configured to protect a motor having a stator and a rotor from overheating, a temperature of a winding is detected by a temperature detection element, such as a thermistor and a thermostat, attached near the winding of the stator and when the detected temperature exceeds a predetermined value, an alarm signal is generated.
Further, a temperature detection device that takes into consideration motor loss in addition to temperature detected by a temperature detector when detecting the temperature of a winding to protect a motor from overheating is also proposed in, for example, Japanese Unexamined Patent Publication (Kokai) No. 2009-261078 (JP2009-261078A).
However, the conventional temperature detection device is configured to protect a winding from overheating and not protect a rotor from overheating. For example, when a rotor of a synchronous motor rotates at high speed, the amount of heat generated in the rotor is excessive and the stator is cooled down forcedly, and therefore, there is a case where the temperature of the rotor becomes remarkably higher than the temperature of the stator. If the temperature of the rotor becomes remarkably higher than the temperature of the stator as described above, there is a problem of causing conduction of heat to a driven object, such as a work and a tool, attached to the motor and there is a problem of causing demagnetization or degaussing of a permanent magnet when the rotor has a permanent magnet.
In order to avoid such a problem, it is necessary to protect not only the winding but also the rotor from overheating. However, the temperature detector, such as a thermistor and a thermostat, performs wired communication, and therefore, it is difficult to incorporate a temperature detector in a rotor in order to detect the temperature of the rotor.